A ram boring machine of this kind is disclosed in German patent specification 21 57 295; it primarily serves to lay supply lines, for example water pipes or cables, beneath streets or embankments or other buildings and obstacles, without the street surface or the surface of the ground having to be torn up simultaneously. This is done by the ram boring machine moving forwards in the ground forcing the earth aside and forming a tunnel behind it into which a supply line can be simultaneously or subsequently drawn.
This known ram boring machine has a two-part housing, i.e. a housing tip screwed into the housing accommodating the striking piston. The housing tip encloses an axially movable chisel with its front end, in the working or striking direction, formed as a striking tip and having at its other end a collar and a shank, the collar being received by a bore in the housing tip. This arrangement of the movable chisel has the advantage that the impact energy of the striking piston can first be transferred positively to the chisel so that greater shattering energy is available. The shank forms the striking surface for the associated striking piston, and in the starting position before the working stroke it projects from a ring screwed into the housing tip in the housing. The ring limits the movement of the collar, and thus of the chisel, counter to the working direction of the striking tip. The movement of the chisel in the working direction is limited by a front stop formed by a widening in the bore in the housing tip accommodating the collar. The chisel is supported on the housing tip by the collar and compression springs; the springs move the chisel from its forward position in the housing tip in the working direction back into its starting position.
Apart from the ram boring machine with the two-part housing described above, ram boring machines are also known in which the housing and the housing tip are in one piece; apart from this there are no substantial differences between a two-part and a one-part machine housing. A common feature of all ram boring machines is that during the forward movement of the ram boring machine the chisel, which breaks up and forces aside the stones or other obstacles, thus clearing a path by impact for the housing moving up behind, is worn considerably owing to the shattering work it has to perform, and must therefore be replaced often.